After Ann Walton-Teter has a double mastectomy, she learns her coverage has been canceled. Anthem Blue Cross admits mistake but timing couldn't have been worse.

Ann Walton-Teter was diagnosed with breast cancer in September. About a month later, she was informed by her health insurer, Anthem Blue Cross, that her coverage had been canceled because of a missed payment.

Anthem would eventually admit that it was mistaken. But Walton-Teter, 43, had to battle the insurance giant to have her coverage restored just as she was recovering from a double mastectomy and preparing for chemotherapy.

In other words, the Santa Monica resident had to go up against a corporate bureaucracy while she was at her weakest and most vulnerable — a situation that plays out time after time nationwide as insurers challenge patients' claims or doctors' prescriptions in the midst of medical crises.

To all those who believe the U.S. healthcare system is second to none, Walton-Teter's case serves as a stark reminder that things can go horrendously wrong even if the patient does everything right.

"It's like they were bullying me to go away," Walton-Teter told me. "You buy insurance in case anything comes up. But when it does, this is how they treat you."

That's not to say all insurers, including Anthem, behave thuggishly whenever customers need them most.

But each time a tale like this arises, it highlights the challenges that can be faced, at the worst possible times, when for-profit companies dig in their heels and insist that they won't cover needed medical procedures.

Unable to land any full-time job with medical benefits, Walton-Teter scraped by, until her illness, with a part-time gig as a surfing instructor that barely allowed her to make ends meet.

Her Anthem insurance policy costs about $350 a month and comes with a $5,900 deductible. Walton-Teter's father makes about half her premium payments because she otherwise wouldn't be able to afford coverage.

She signed up with Anthem in 2008. At the time, Walton-Teter had no preexisting conditions or medical issues to speak of. There was a history of breast cancer in her family, but she disclosed that on her insurance application.

If Anthem had taken a close look at her medical files, it would even have seen that in 2004 Walton-Teter tested positive for BRCA1, a genetic marker indicating a higher likelihood of breast cancer.

"I feel that Anthem received a full disclosure of my medical history," Walton-Teter said.

She was diagnosed with an aggressive form of breast cancer Sept. 4. Three weeks later, she underwent a double mastectomy.

And just a few weeks after that, Walton-Teter received the letter from Anthem informing her that her coverage had been canceled "for nonpayment of a premium."

Despite her weakened condition, she had to scrounge up the documentation to prove that she'd met her side of the bargain. Walton-Teter also had to run the obstacle course of Anthem's customer-service system.

"They kept giving me the runaround," she said. "I was on hold for an hour at a time."

Anthem also told her doctor that Walton-Teter was uninsured as she had to start laying the groundwork for the chemotherapy treatments that began last month, causing an additional layer of anxiety and confusion.

Walton-Teter said the company only discovered that she had indeed made all her payments once she started lodging complaints with state insurance regulators.

"It seemed like they were determined to do their damnedest to make me give up," Walton-Teter said.

Did Anthem ever apologize?

"No, they never apologized."

Kristin Binns, an Anthem spokeswoman, acknowledged that the situation resulted from "an error on our part." She said Walton-Teter's account was not properly credited with a monthly payment.

"When we realized the error, her payment was properly credited and no lapse in coverage occurred," Binns said.

She added that, according to Anthem's records, Walton-Teter has never had a claim rejected by the insurance company.

Perhaps, as Anthem says, this was just a clerical error. Stuff happens.

But Walton-Teter thinks the timing was strange. All was well with her coverage until she was diagnosed with cancer. Then, suddenly, Anthem had a problem with her payments and immediately canceled her policy.

"Wouldn't you be suspicious?" Walton-Teter asked.

I think anyone in her position would be.

Even if we give Anthem the benefit of the doubt, what happened to Walton-Teter illustrates how easily the insurance safeguards we take for granted can vanish. Our healthcare system offers precious few guarantees.

No matter who wins Tuesday's presidential election, there's still much work to be done in protecting those who have insurance, not to mention extending coverage to the 50 million who go without.

I know this much: Walton-Teter won't be the last person to face the experience of losing coverage when she instead needs the healthcare system to be there for her.

And that's just cruel.

David Lazarus' column runs Tuesdays and Fridays. He also can be seen daily on KTLA-TV Channel 5 and followed on Twitter @Davidlaz. Send tips or feedback to david.lazarus@latimes.com.